I have the same issue. A free app for demo purposes worked fine last week, suddenly wouldn't resume (with no changes) earlier this week. Now with a, seemingly succesful, redeployment I get the 404 error when clicking on 'View App'
Same here, and I have no clue what is happening. In my case, it's almost as if the openid/login request handler is just not active.. it's the immediate response after clicking on log in through mendix sso -> 404 not found.